This invention relates to a yarn tightening element comprising a passage for a yarn and a contact part to transmit a tension to a yarn moving along through this passage.
Similar yarn tightening elements are generally known as plates for keeping tight and if required to withdraw warp yarns conducted to the weaving machine from respective bobbins on a weaving creel. Keeping these warp yarns tight is necessary in order to avoid them from getting mutually entangled. Slack warp yarns in the weaving zone should be absolutely avoided, because they will have a negative effect on the quality of weaving. The consequence might be an irregular formation of the pile. It should also be possible to withdraw from the weaving zone warp yarns taking up different positions in the shed during the weaving process in order to keep them tight.
A known type of weaving creel plates is described in the Belgian patent application n(09900475. These plates have an elongated body of a limited thickness, being the dimension in a direction transverse to the direction of movement of the warp yarns, when using the plate, so that they take up only limited space in the said direction. The contact means is carried out as a small cable wheel, rotatably mounted in the interspace between two flank plates.
Each plate co-operates with a respective warp yarn in order to tighten it. In doing so, the warp yarn extends through the passage below the small cable wheel and between the flank plates. With its small cable wheel, the plate rests on the warp yarn, and by its weight, exerts a downwards directed tractive force on that warp yarn, so that it is tightened and withdrawn if needed. This tractive force may be increased, for instance, to adapt it to certain modified properties (thickness, flexibility . . . ) of the warp yarns being used, by hanging an additional weight on the plate. For that purpose, the bottom part of the plate is provided with a hook.
However, these known plates have the following disadvantages. In order to put such a plate on a warp yarn in an operational position, the warp yarn should be cut through so that a free end can be pulled through the said passage between the flank plates, after which the free ends have to be tied together again. Also to remove such a plate from a warp yarn the warp yarn must be cut through and, after having removed the plate, the yarn ends have to be tied up again. Therefore installing or removing the plates is a very complicated and time-consuming job. Installing a yarn tightening device of a weaving creel, making use of a series of such plates, requires especially long installing times and hence it is rather expensive.
It is a purpose of this invention to provide a yarn tightening element, which comprises a passage and a contact means for transmitting a tightening force to a yarn moving through this passage, allowing to remedy the disadvantages mentioned above of the known yarn tightening elements and devices. It is at the same time likewise a purpose to provide a user-friendly yarn tightening element being of a simple design.
According to this invention, the purposes mentioned above are attained in an efficient manner by providing a yarn tightening element comprising a passage for a yarn and a contact means for transmitting a tightening force to a yarn moving through this passage, the passage of whichxe2x80x94according to this inventionxe2x80x94on at least one side of the plane of movement of the yarn comprises a boundary, interrupted across its width, so that via that interruption a part of the yarn moving through from that side of the plane of movement may be brought to co-operate with a contact element, and that the boundary (boundaries) of the said passage is/are carried out in such a manner that they extend up to alongside the yarn when using the yarn tightening element.
At the same time, the interruption should not necessarily run according to the direction of movement of the yarn and even should not necessarily have a rectilinear course. It is only important that the boundary has an interruption over the entire width through which a yarn may be brought within the boundary.
In this description and in the claims, by a xe2x80x9cboundary interrupted across its widthxe2x80x9d is meant a boundary that has a continuous interruption across its entire width. The lateral direction is the direction that is almost parallel with the plane of movement of the yarn when using the yarn tightening element.
In this description and in the claims, by a xe2x80x9cpassage for a yarnxe2x80x9d is meant each space through which a yarn may extend in co-operation with a yarn. This space may be not bordered or entirely or partly bordered on one or several sides or entirely bordered on all sides.
A similar yarn tightening element can be installed on a yarn in its operational position by an ordinary hooking on movement and be removed again by an equally simple hooking off movement. When doing so, the yarn running through will be made to co-operate with the contact means via the interruption in the boundary. To this end, the yarn should, of course, no longer be cut through. Hooking on and hooking off the yarn tightening elements can be done very quickly and is a very simple operation. Therefore, such a yarn tightening element is very user-friendly. Moreover, a yarn tightening element having the characteristics of this invention can be of a very simple design, so that it can be produced also very easily and cheap, for instance by means of parts made of synthetic material.
Because the boundary (boundaries) of the said passage extend up to along the yarn, when using the yarn tightening element, an optimum guidance of the yarn is obtained and an undesired lateral movement of the yarn tightening element with respect to the yarn is no longer possible, so that the contact element and the yarn are always kept in a position in which they co-operate.
In a preferred embodiment, the yarn tightening element comprises a boundary on both sides of the plane of movement of the yarn, whereas this boundary is interrupted across its entire width on at least one side of this plane of movement. A similar embodiment with a boundary on both sides of the yarn passage has the advantage that the boundary provides a guidance of the yarn and, among others, will assist to preserve the co-operation between the contact element and the yarn when using the yarn tightening element. If the contact element is carried out in the form of a small guiding wheel, the boundary on both sides will help to avoid the small wheel from running off the yarn.
An additional advantage of this boundary on both sides is that inconvenient oscillating movements of the yarn tightening element resting on the yarn will be avoided or reduced to a large extent. A similar yarn tightening element is particularly reliable.
Preferably, the said boundary is formed by one or more fingers directed downwards, whereas the said interruption of this boundary is formed between the extremities of each finger and a part of the yarn tightening element. In a particular embodiment, this boundary is formed by two such fingers, being kept separated from one another in the direction of movement of the yarn.
For the contact means, preferably a rotatable guiding wheel is provided, guaranteeing minimal friction of the yarn in the yarn passage of the yarn tightening element.
The yarn tightening element according to this invention may be provided for a device in which the tractive force is caused, entirely or partly, by a spring force, or any other force. However, an embodiment of the yarn tightening element, provided to exert the said tractive force by gravity, more particularly by the yarn tightening element""s own weight is preferred. Such a device is indeed very simple and reliable.
Preferably, care is taken that the yarn tightening element comprises a weight element that is removable. So, the tension may be influenced in a very simple manner by replacing a first weight element by another weight element (having a different weight). In order that the yarn tightening element will require the smallest possible space in a direction at right angles to the plane of movement of the yarn, this removable weight element is carried out as a plate-shaped body. Because of the limited thickness of such a weight element, the warp yarn can run very closely next to one another and a great number of yarns may be provided beside one another at a useful width.
Preferably, the yarn tightening element comprises also a holder and a weight element additional to the said contact means, while both the weight element and the contact means are carried by the holder. In this manner, a very simple construction is obtained the parts of which (being very restricted in number anyway) are easily to produce and to assemble.
If the yarn tightening element is composed of parts that may be connected by hand without the help of tools, it is rather simple to assemble the yarn tightening elements. This may be done, for instance, on an automatic assembly line. In case dismantling can also occur by hand, replacing a part can be done very quickly without the use of any tools. Such a yarn tightening element is very user-friendly.
In a particularly preferred embodiment, the holder and the contact element are made of synthetic material, while the weight element is made of metal. Manufacturing parts of synthetic material can occur at very low production costs. Yet, by using metal for the weight element, a sufficiently heavy weight can be obtained at a relatively small volume. Moreover, metal has the advantage of a good electrical conductivity, so that the yarn tightening element can be used to realize an electric contact in one or more positions, for instance, to detect these positions and the corresponding yarn tension.
For instance, in order to realize such a contact, the yarn tightening element can be made with a recess, at least one edge of which is provided to make contact with a contact element of a detection device in a pre-determined position of the yarn tightening element.
Another disadvantage of the known plates described above is, that adapting its weight should occur by hanging weight unto the bottom part of the plate. Because of this, the height of the plate will increase, and consequently the useful height for moving up and down the plates will be reduced. Only weights of a limited height may be suspended from the plate. The heavier the weights are, the longer they are, so that a number of weights can no longer be used because they are becoming too long.
An additional purpose consists in providing a yarn tightening element having one or more characteristics of the present invention, but for which at the same time a number of weight elements are provided, that can be used irrespective of their weight.
This purpose is attained by providing a yarn tightening element according to this invention, where at least two weight elements of different weights have been provided, these weight elements having virtually the same height. The weight elements have a height (irrespective of their weight) that is adapted to the space available. Adapting the exerted tightening force has no longer any influence whatsoever on the height of the yarn tightening elements.
Similar weight elements may also be used with yarn tightening elements that are not carried out in accordance with this invention. Since, with these other (known) types of yarn tightening elements, the advantage mentioned above can also be obtained.
Preferably, the difference in weight of the weight elements is mainly caused by the fact that they have different dimensions in the direction running almost parallel with said plane of movement of the yarn in the operational position of the yarn tightening element. Since the available space is not only limited as to height, but also in a direction transverse to the direction of movement of the yarn, in order to be able to maintain a minimum distance between yarns running next to each other, so that also an increase in thickness of the weight elements is not desirable. The only direction where sufficient space is still available is the direction parallel with the plane of movement of the yarn. The difference in weight of the weight elements may be obtained by changing their dimensions in that direction (their width).
Moreover, the weight elements can be attached in such a manner that they extend along the other parts and therefore do not increase the height of the plate.
Of course, a number of parts for composing the yarn tightening element according to this invention are within the scope of the present invention. This is particularly true for a yarn tightening element with one or more additional weight elements having the above-mentioned characteristics, which are provided to modify the weight of the yarn tightening element.
Now, this invention will be further explained with the help of the following detailed description of a preferred yarn tightening plate according to this invention. The intention of this description is exclusively to give an explanatory example and to indicate further advantages and particulars of the present invention and may in no way be interpreted as a limitation of the scope of the present invention or of the patent rights claimed in the claims.